In one sense, President Trump should be happy with how the 2018 election is shaping up: It’s all about him. In another sense … he should not be happy about that.

We’ve known for a while that the election would be, to some extent, a referendum on Trump’s presidency. We knew that, really, before we knew that Trump would be president. The first midterm elections after a new president is inaugurated have often hinged on perceptions of that president, and had Hillary Clinton prevailed two years ago, we would be assessing how Americans felt about her right about now.

But it still seems different to consider Trump’s role, simply because he’s been so effective at keeping himself in the center of the political conversation and so insistent that his party will emerge victorious in November.

Trump, as we’ve noted before, inspires much stronger feelings than have past presidents. Washington Post-ABC News polling since 2000 shows that, with the exception of George W. Bush in the 9/11 era, the percent of Americans with strongly supportive or strongly disapproving opinions of Trump is higher than for his immediate predecessors.

And most of those opinions are negative.

We see this in a new poll from NBC News and the Wall Street Journal. Two thirds of Americans have strong opinions of Trump; more than 4 in 10 Americans have strongly negative views.

That poll is interesting, too, because it sought to translate those feelings into attitudes about the midterm elections. Of the five factors the pollsters explored as possible motivators for a vote, none was more motivating for earning a voter’s support than a willingness to act as a check on Trump. Voters were 25 percentage points more likely to say that a candidate acting as a check would increase the likelihood of their vote than it would decrease it.

Nearly half of voters said that would make them more likely to support a candidate. At the same time, half said that a candidate who supports Trump’s immigration policies or who regularly voted with Trump would be less likely to earn their support. As our Greg Sargent notes, a majority of voters in competitive House districts want members of Congress willing to act as a check on Trump.

Perhaps the most interesting part of this poll, though, is that more than a quarter of Republicans want candidates who will act as a check on Trump. On net, Republicans were 11 points more likely to say that they would be turned off by a candidate acting as a check on Trump, but it’s still the case that 27 percent would be encouraged to vote for a candidate willing to check Trump. That even as Republicans support candidates who support Trump on policy issues. By more than 60 percentage points, Republicans are more likely to support candidates that stand with Trump on taxes and immigration. But they’re nearly split on candidates who stand up to Trump generally.

That’s an important distinction. A candidate can stand up to Trump while still voting with him. Candidates willing to act as a check on Trump are not necessarily Democrats, though Democrats are certainly more likely to hold that position.

This is important, though, because of Trump’s somewhat precarious position. Should the investigation by special counsel Robert S. Mueller III head south, Trump could increasingly be at risk for softening support on Capitol Hill. Even as it stands, a quarter of his party (and 4 in 10 independents and 7 in 10 Democrats) are looking for candidates willing to check Trump’s power. If new questions arise about Russian coordination or other issues, those numbers could increase. Republicans on Capitol Hill up for reelection in November could face new pressure to hold Trump accountable, especially in swing districts with more Democratic and independent voters.

Trump is still popular with Republicans and still enjoys strong support from a quarter of the population (per that NBC-Journal poll). The last thing he wants, though, is more people in Congress willing to act as a check on his power. Unfortunately for him, that’s one of the most important things voters want.